The present invention relates radio communications systems, and more particularly to digital radio communications systems. Even more particularly, the present invention relates to multiple modulations in a radio communications system.
Radio communications devices are commonly known in the art of communications. A radio is a device that transmits and receives electromagnetic energy being within the range of frequencies known as radio frequency. Radios are commonly used in communications systems as a means to transmit and receive communications over a wireless communications link. Prior art radios have many applications, such as in FM broadcast radio, mobile cellular communications, point to point communications systems, and point to multipoint communications systems.
Radios typically consist of a radio transceiver that is responsible for producing the radio frequency power for transmission and receiving radio signals from other radio transceivers. Radios also include frequency converters that converts baseband signals to a radio frequency for transmission and converts received radio frequency signals back to baseband signals.
An important part of the radio is the modem, or modulator/demodulator unit. The modem modulates the baseband signals to the carrier frequency as is commonly known in the art. This changes the format of the baseband signal to a format that can travel great distances, as opposed to the baseband signal which has a very limited range. The modem also demodulates the modulated signals at the receiving radio. There are many different types of modulations that radios typically take advantage of, e.g. frequency modulation, amplitude modulation, phase modulation, etc. In addition, there are many types of modulations within each general modulation. For example, phase modulation includes phase shift keying, quadrature phase shift keying, quadrature amplitude modulation, etc. Prior art radios typically have a modem that operates using only one modulation mode.
In some radio applications, such as a point to multipoint microwave radio communications system, it is advantageous to use different radios, wherein each radio uses a different modulation scheme. In a prior art point to multipoint communications, a fixed location central hub site contains radios that communicate with corresponding radios at fixed location remote sites. The fixed location remote sites are physically located at different distances from the hub site. Thus, the communications system is a point (hub site) to multipoint (many remote sites) communications system. Additionally, microwave radio signals, due to their extremely high frequencies, are limited by line of sight and distance from the radio transmitter.
Consequently, a radio using one modulation mode will transmit a radio signal that will propagate or travel a different distance than a radio using a different modulation. Thus, in such a point to multipoint communications system, a first radio using a first modulation mode may only be able to communicate with the radios at the remote sites that are closest to hub site and be within an acceptable bit error rate (BER), but the bit error rate may be unacceptable to the radios at the remote sites that are farther away from the hub site. Thus, a second radio using a second modulation is needed to communicate with the radios at the farther located remote sites, since the first radio only communicates using the one modulation mode. Additionally, a third radio using a third modulation may be needed to communicate with radios at remote sites outside of the range of the second radio. Alternatively, the third radio could be used to communicate with the radios at all of the remote sites; however, the third radio uses a modulation mode that requires more bandwidth than the first or second radio to transmit signals, which does not allow for efficient use of the communications link. Therefore, disadvantageously, different radios, each using modems that support one modulation mode, are needed at the hub site to communicate with the radios located at remote sites which are varying distances from the hub site.
The present invention advantageously addresses the needs above as well as other needs by providing a multi-modulation radio including a multi-modulation modem, and related methods of radio communication, that support multiple modulations within a single radio unit.
In one embodiment, the present invention can be characterized as a radio comprising a multi-modulation modem, wherein the multi-modulation modem includes a modulator that modulates signals using a plurality of modulations. The radio also comprises a frequency converter coupled to the multi-modulation modem for converting the signals to a radio frequency and a transceiver unit including an antenna coupled to the frequency converter for transmitting the signals over a radio communications link.
In a further embodiment, the present invention can be characterized as a modem comprising a multi-modulation modem. The multi-modulation modem includes a modulator that includes a modulation selector unit. The modulator modulates signals using a plurality of modulations and the modulation selector unit selects respective ones of the plurality of modulations to modulate the signals. The multi-modulation modem also includes a demodulator for demodulating the signals using the plurality of modulation modes.
In an additional embodiment, the present invention can be characterized as a method, and means for accomplishing the method, of radio transmission comprising the steps of: receiving signals into a radio; modulating the signals using respective ones of a plurality of modulations; converting the signals, having been modulated, to a radio frequency; and transmitting the signals over a radio communications link.
In yet another embodiment, the present invention can be characterized as a method, and means for accomplishing the method, of radio reception comprising the steps of: receiving signals from a radio communications link into a radio, wherein the signals are modulated with respective ones of a plurality of modulations; converting the signals from a radio frequency to a digital baseband; and demodulating the signals having been modulated with the respective ones of the plurality of modulations.
In a further embodiment, the present invention can be characterized as a method of modulation comprising the steps of: receiving signals into a modulator; converting the signals to symbols; formatting the symbols into bursts; mapping the bursts into respective ones of a plurality of constellations, wherein each of the plurality of constellations corresponds to a respective one of a plurality of modulations; and modulating the bursts using respective ones of the plurality of modulations.
In a supplementary embodiment, the present invention can be characterized as a method of demodulation comprising the steps of: receiving complex symbols into a demodulator, wherein the complex symbols have been modulated using respective ones of a plurality of modulations; obtaining a gain estimate of the complex symbols having been received; obtaining a timing estimate of the complex symbols having been received; obtaining a phase estimate of the complex symbols having been received; obtaining a frequency offset estimate of the complex symbols having been received; minimizing intersymbol interference using an equalizer; and mapping, using a multi-modulation slicer, the complex symbols to respective ones of a plurality of constellations, wherein each of the plurality of constellations corresponds to a respective one of the plurality of modulations.
In an additional embodiment, the present invention can be characterized as a method of providing accurate parameter estimates of received complex symbols in a demodulator comprising the steps of: receiving complex symbols from a burst into a demodulator, the burst having been transmitted over a communications channel; loading stored interpolation coefficients into a precorrelation filter, wherein the stored interpolation coefficients represent a true timing offset of the communications channel as seen by the demodulator, whereby the communications channel has been equalized; correlating the received complex symbols from the burst using the precorrelation filter having been loaded; detecting the burst; and estimating parameters of the burst having been detected, whereby the estimating step is performed with the communications channel having been equalized.
In a further additional embodiment, the present invention can be characterized as an acquisition section of a demodulator for allowing accurate parameter estimation. The acquisition section includes a precorrelation filter for receiving complex symbols comprising bursts, wherein the bursts have been transmitted over a communications channel, a burst detector coupled to the precorrelation filter, and a parameter estimator coupled to the burst detector. The acquisition section also includes an equalizer coupled to the parameter estimator and a coefficient memory coupled to the equalizer and the precorrelation filter.